1. Field of the Invention
The present invention relates to technology for accessing storage media, and in particular, to a signal decoder, a signal decoding method and a storage system.
2. Description of the Related Art
In recent years, storage devices using hard disks are becoming essential devices in various fields, such as those of personal computers, hard disk recorders, video cameras, mobile telephones, and the like. Various specifications are required for the storage devices using hard disks, according to fields of application; for example, when used in personal computers, high speed and large capacity are required. However, since the amount of data to be handled increases as the capacity is enlarged, correction of generated errors by error correction processing becomes a bottleneck for realizing high speed.
Conventionally, Reed-Solomon encoding, turbo encoding, low density parity check encoding, and the like, are used as error correction methods employed in storage devices using hard disks. Common to all of these error correction encoding methods is the fact that they are strong with regard to randomly generated errors, but are weak with regard to errors generated in groups. For example, when data of 10,000 bits is composed of 10 blocks of code words, that is, when each code word is 1000 bits, with 100 bit burst errors, there is a tendency for errors in certain code words. In these types of cases, even if error correction decoding is carried out, errors cannot be corrected. Thus, additional processing of re-reading, re-decoding, and the like, occurs, and as a result, there is an effect on reading speed. As a method of improving this, carrying out interleaving may be considered. Since interleaving is composed of processing for interchanging data order, an effect is realized of dispersing errors occurring in groups, and changing them into random errors (for example, refer to Patent Document 1).
Patent Document 1: Japanese Patent Application, Laid Open No. 2002-367296
In view of these conditions, the inventors came to recognize the following problem. That is, when interleaving is carried out, it is necessary to decide in advance in what way data series are sorted, and since it is necessary to perform interleaving for each of writing to and reading from the storage device, there is a problem in that it is difficult to adaptably change sorting rules.